The present invention relates, in general, to a traction drive for a starter-generator unit of an internal combustion engine, and more particularly to a tensioning device for the traction drive.
A traction drive of a type involved here may include a first pulley which is operatively connected to the crankshaft of the internal combustion engine, a second pulley which is operatively connected to the starter-generator, and a tensioning device for biasing the pulling strand and the return strand of the traction drive. The starter-generator is a structural component to start the internal combustion engine in dependence on the operating mode, or to generate electric energy while the internal combustion engine is running. Thus, the starter-generator assumes the function of a starter as well as the function of a generator. Depending on the respective operating mode, the starter-generator or the internal combustion engine introduces a torque into the traction drive, resulting in a swap between the return strand and the pulling strand in the traction drive. As a consequence of the directional change of the torque, the tensioning device requires two tension pulleys for sufficiently tension the respective return strand of the traction drive.
Japanese patent publication JP 09 144 821 A1 describes a traction drive with a tensioning device having two tension pulleys associated to a return strand or a pulling strand. This conventional traction drive has a driving pulley and a driven pulley of same dimension and connected by a belt as traction member. The tensioning device includes a straight arm which is fixedly supported in midsection thereof and has opposite ends for respectively supporting the tension pulleys in symmetric relationship, whereby one tension pulley is associated to the pulling strand and the other tension pulley is associated to the return strand. A spring member is hooked on one end side of the arm to force the tension pulleys of the tensioning device against the belt. As the tension pulleys of the tensioning device have a same size and as a result of the symmetric support, the wrap angle of the belt about the tension pulleys is, as a consequence of the spring member, identical, when the traction drive is in operating mode.
It would be desirable and advantageous to provide a traction drive with improved tensioning device which sufficiently tensions the traction member, regardless of the direction of the torque being introduced into the traction drive.